The present invention relates to a radio frequency module on which a radio frequency semiconductor integrated circuit is to be mounted for use in radio communications, and to a method for manufacturing such a radio frequency module.
There is conventionally known a radio frequency module forming a waveguide in a multi-layer substrate, as described in 1999 IEEE MTT-S Microwave International Symposium Digest, pp. 453-456. In this structure, conductors are provided on the both surfaces of a multi-layered dielectric substrate. An air gap, constituting a waveguide, is formed in the dielectric substrate to provide through-holes in wall regions of the air gap. Meanwhile, conductors are provided between the layers of the dielectric substrate, to form waveguide walls in a lattice form using the through-holes and conductors. The air gap in the dielectric substrate serves as a waveguide defined by the upper and lower conductors and the lattice-formed walls, allowing a radio frequency to propagate.
In this radio frequency module, the waveguide on-wall conductor is formed in a lattice by the through-holes and the conductors. In a basic propagation mode TE10 of the waveguide, a current flows parallel with a traveling direction of a radio wave relative to the waveguide wall, raising a problem that conductor loss is increased by a discontinuity resulting from a lattice-formed structure of the wall conductor. With respect to this problem, such loss can be reduced by providing through-holes sufficiently short relative to the wavelength or by increasing the number of layers in the multi-layer substrate. In a millimeter-wave band, however, the wavelength in a free space ranges from 10 millimeters to 1 millimeter. Consequently, the discontinuity on the wall surface is not negligible relative to the wavelength, and hence loss inevitably increases. In particular, because the wavelength in a dielectric substrate is inversely proportional to a square root of an effective relative dielectric constant, the effect increases furthermore.
Meanwhile, the conventional rectangular waveguide is manufactured by metalworking. This, however, incurs a problem to increase material cost and time required in working.
The present invention is to solve the foregoing problem, and it is an object to provide a radio frequency module having a waveguide circuit which is reduced in loss of a radio frequency current flowing through a wall surface thereof, excellent in connectability to other circuits and low in cost but high in performance.
It is another object of the present invention to provide a manufacturing method thereof.
A radio frequency module of the present invention comprises: a dielectric substrate having first and second main surfaces and a rectangular penetration hole opening in the first and second main surfaces; first and second conductors for grounding respectively provided on the first and second main surfaces to cover the openings of the penetration hole; and a conductor layer formed on opposite inner wall surfaces in the penetration hole of the dielectric substrate; whereby a waveguide structure is configured by the first and second conductors and the conductor layers.
According to the radio frequency module, by structuring a wall surface of the waveguide using dielectric with a continuous conductor material surrounding the same, it is possible to reduce the loss of a radio frequency current flowing through the wall surface. The dielectric substrate itself, in a planar structure, is excellent in connectability to other circuits. In forming a wall-surface conductor, there is no need to form through-holes or making a substrate with layers. It is accordingly possible to realize a radio frequency module having a waveguide circuit that is low in cost but high in performance.
Meanwhile, the method for manufacturing a radio frequency module comprising the steps of: forming, by laser forming, a penetration hole having a plurality of rectangular portions coupled one with another in a first dielectric substrate formed, on a first main surface, with a conductor to reach the conductor; forming a metal film on an inner wall surface of the penetration hole; and joining a second dielectric substrate forming a conductor on one surface and an input/output line on the other surface, at the conductor surface, onto the other surface of the first dielectric substrate forming the metal film through a conductive double-sided adhesive sheet worked with a blank hole in a form of the penetration hole.
According to the manufacturing method, it is possible to realize, in a waveguide structure formed in a dielectric substrate, a continuous wall-surface structure for reducing conductor loss by a general working process at low cost and on a mass-production basis.